An LED consists of a semiconductor junction, which emits light due to a current flowing through the junction. At first sight, it would seem that LEDs should make an excellent replacement for the traditional tungsten filament incandescent bulb. At equal power, they give far more light output than do incandescent bulbs, or, what is the same thing, they use much less power for equal light; and their operational life is orders of magnitude larger, namely, 10-100 thousand hours vs. 1-2 thousand hours.
However, LEDs have a number of drawbacks that have prevented them, so far, from being widely adopted as incandescent replacements. Among the chief of these is that, although LEDs require substantially less power for a given light output than do incandescent bulbs, it still takes many watts to generate adequate light for illumination. Whereas the tungsten filament in an incandescent bulb operates at a temperature of approximately 3000K, an LED, being a semiconductor, cannot be allowed to get hotter than approximately 120° C. The LED thus has a substantial heat problem: If operated in vacuum like an incandescent, or even in air, it would rapidly get too hot and fail. This has limited available LED bulbs to very low power (<approximately 3 W), producing insufficient illumination for incandescent replacements.
One possible solution to this problem is to use a large metallic heatsink, attached to the LEDs. This heatsink would then extend out away from the bulb, removing the heat from the LEDs. This solution is undesirable, because of the common perception that customers will not use a bulb that is shaped radically differently from the traditional shaped incandescent bulb; and also from the consideration that the heatsink may make it impossible for the bulb to fit in to pre-existing fixtures.
More recently, a means for cooling LEDs in light bulbs have had the LEDs immersed in a fluid, a gel or a plastic (PCT/US07/10470 and PCT/US07/10469). The fluid, gel or plastic provides a high thermal conductivity path from the LED heat sources to the bulb's surface and the ambient.
In some cases, however, the thermal conductivity of the fluid, gel or plastic may still not be high enough to maintain the LEDs at their desirable operating temperature. This is true especially when using individual high-power LEDs as opposed to using many low-power LEDs. For these applications, then, it would be desirable to find a material that had even higher thermal conductivity or could be combined with these materials to achieve higher thermal conductivity, but that at the same time maintained the desirable characteristics of the fluid, gel or plastic, that is, low optical loss, and potentially electrical insulation.